1. FielD of the Invention
The present invention relates generally to a fluid pump, such as that applicable for a hydraulic circuit of an automotive power steering device. More specifically, the invention relates to a fluid pump which can regulate a fluid flow rate of a working fluid to be supplied to a hydraulic device.
2. Description of the Background Art
One of the typical constructions of the fluid pump has been disclosed in Japanese Utility Model First (unexamined) Publication (Jikkai) Shows 57-79278. The disclosed fluid pump has a drive shaft associated with an automotive engine to be rotatingly driven by means of the latter. The drive shaft carries a rotor for rotation therewith. The rotor is rotatably disposed within a cam ring. The rotor is formed with a plurality of essentially radially extending grooves. A plurality of vanes are thrustingly disposed within the grooves so as to move toward and away from the inner periphery of the cam ring. The vanes projecting from the grooves and are in sliding contact with the inner periphery of the cam ring defining a working chamber between the adjacent vanes. As is well known, the cam ring is formed on an oval or elliptic configuration so as to define two sets of induction ranges for increasing working chamber volume to introduce the working fluid and a compression range for decreasing working chamber volume to pressurize the working fluid within the working chamber. The working chamber at a predetermined angular position communicates with a high pressure chamber. Part of the pressurized fluid is introduced into the vane grooves from radial insides of the rotor so as to bias the vanes toward the inner periphery of the cam ring.
The high pressure chamber is connected to a supply line connected to an external hydraulic device, such as the automotive power steering device to supply the pressurized fluid therethrough. The supply line is connected to a high pressure path. The high pressure path is connected to a low pressure chamber via a flow control valve. The high pressure path is also connected to a spool chamber. A spool valve disposed within the spool chamber is operable in response to the internal pressure within the spool chamber and a pressure in a pressure responsive orifice. By this construction excessive pressure in the high pressure chamber is fed back to the low pressure chamber.
In such a fluid pump arrangement, the supply line is connected to the high pressure path in the vicinity of the high pressure chamber in a direction perpendicular to the flow direction of the working fluid in the high pressure chamber. With such construction, the discharge rate of the fluid pump is increased proportional to the engine revolution speed. When increasing the flow amount to be discharged, the fluid pressure in the high pressure chamber serves as resistance. Therefore, the pressure difference between the fluid pressure in the spool chamber and the pressure responsive orifice becomes greater to cause a greater gradient of pressure variation. This causes a substantial variation of the fluid pressure to be supplied to the hydraulic device when engine speed varies due to gear shifting. Therefore, flow control by means of a pressure control valve in a power steering control circuit becomes unstable to cause degradation of the vehicular steering characteristics.